1. Field of Invention
This invention relates to a thermochromic composition and an electron-accepting compound, which has a good sensitivity as metachromatizing temperature change.
2. Description of Related Art
With regard to reversible thermochromic compositions capable of causing reversible metachromatism In a specific temperature range upon electron-donating/accepting reaction,.some proposals are disclosed In, e.g., U.S. Pat. Nos. 4,028,118, 4,138,357, and 4,425,161.
In the present, several materials or compositions were known as reversible thermochromic material such as (1) materials utilizing a crystal of a metal complex, (2) materials utilizing a cholesteric liquid crystal, (3) compositions having as three constituents thereof an electron-donating color former, a chemical compound having a phenolic hydroxyl radical and a chemical compound having an alcoholic hydroxyl radical, (U.S. Pat. Nos. 2,324,671, 3,560,229, and 4,028,118), and (4) compositions containing a polyhydroxy compound, an alkali metal salt of boric acid and a pH indicator.
Of these reversible thermochromic materials, (1) the one using a crystal of metal complex is superior in heat resistant and light resistant properties and is partly utilized for industrial use, but its metachromatizing temperature is higher than room temperature and it further has the defect that its chromic hue is limited. (2) Cholesteric liquid crystals are used for thermometers, ornaments and daily necessaries, but its metachromatizing temperature cannot be freely selected and also it is expensive and has the defect that its metachromatism life is short. (3) The combination of an electron-donating color former and 2,2-bis-(4-hydroxyphenyl)propane (hereafter called bis-phenol A) is widely used in stationeries, toys, clothing and the like, but its usage is limited because of its poor light resistance, and (4) the combination of a polyhydroxy compound, an alkali metal salt of boric acid and a pH indicator has the problem that its usage is limited because its metachromatism temperature is high and some time is required for it to chromically respond to temperature change.
It is an object of the invention to produce a reversible thermochromic composition excellent in terms of developing color density resulting from thermochromic transition.
It is another object of the Invention to produce an encapsulated thermochromic composition suited for effective utilization of other Industry fields.
In accordance with the foregoing and other objectives of the present invention, the present invention provides a reversible thermochromic composition comprising (a) an electron-donating color former, (b) an electron-accepting compound represented by Formula I 
wherein R1 represents a straight-chain or a branch-chain alkyl group having 1 to 3 carbon atoms, R2 represents an alkyl group, an aromatic group or a heterocyclic group having 1 to 14 carbon atoms, (c) a solvent comprising alcohol, amide, ester, ether, or ketone, (d) a light stabilizer. The components mentioned above are enclosed in a microcapsule. Furthermore, the reversible thermochromic composition undergoes reversible metachromatism at a temperature within the range of xe2x88x9250xc2x0 C. to 80xc2x0 C.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.